As an energy source substituting fossil fuels, a solar cell using sunlight is drawing attention and being studied in various ways. Patent Literature No. 1 to 3 disclose, as an example of a solar cell, a dye-sensitized solar cell exploiting photoinduced electron transfer of a metal complex.
The dye-sensitized solar cell has a module in which a porous light reflecting layer, a porous insulating layer, and a conductive layer (counter electrode) are laminated in this order on a porous semiconductor layer (power generating layer) onto which a dye is adsorbed as disclosed in Patent Literature No. 4. The dye is excited with visible light, and the resulting electrons are transferred to the porous semiconductor layer, whereby power is generated. Accordingly, in order to improve photoelectric conversion efficiency of the dye-sensitized solar cell, a large amount of dye needs to be adsorbed onto the surface of the porous semiconductor layer constituted with oxide semiconductor particles.
As a method for causing more dye to be adsorbed onto surfaces of oxide semiconductor particles, for example, there is a method of increasing the specific surface area of the oxide semiconductor particles by reducing the diameter of the particles.
However, if micro-sized oxide semiconductor particles are used, the number of contact points between the particles is increased, and hence the electrical resistance of the porous semiconductor layer increases. Consequently, electron transfer efficiency is reduced, and this leads to a problem of reduction of photoelectric conversion efficiency.
Patent Literature No. 5 suggests, as a method for solving the above problem, a method of causing the porous semiconductor layer to contain light scattering particles having a particle size of about 20 nm to 100 nm that is larger than the particle size of the oxide semiconductor particles.